1. Field of the Invention
The present invention relates to a data transfer system that transfers control data to a predetermined apparatus via a data transfer apparatus and, more particularly, to a data transfer system that transfers a large volume of control data at high speed.
2. Related Background of the Invention
When a large volume of control data generated in a control workstation is transferred to an apparatus to be controlled via a data transfer apparatus, a high-speed data transfer is required in order to improve total throughput.
An example of an electron beam drawing apparatus is described as the apparatus to be controlled. Conventionally, for the connection processing between a control workstation and an interface of a data transfer apparatus, a data transfer system (data transfer method, electron beam apparatus) has been proposed. Japanese Unexamined Patent Publication (Kokai) No. 2005-94412 (claim 1, page 4) is an example of the prior art. In this prior art a subcommand, which is a set of a data transfer command and data to be written to a specified address, and a compound command having a compound command header including the number of subcommands, number of words, control bytes, transfer time of information, etc., are formed into one frame and the frame is transmitted to the interface, and after the transmission is completed, a response command is transmitted from the interface to the control workstation.
According to the system, it is possible to increase the effective transfer rate because the connection processing for each time of transfer of command data is no longer necessary.
The conventional data transfer system (refer to FIG. 5) described above relates to the connection processing between a control workstation 4 and a data transfer apparatus 5, however, recently, even shot expansion is performed on the side of a data transfer apparatus, and therefore, in order to improve the throughput of the entire system, it is also necessary to increase the data transfer rate between the data transfer apparatus 5 and an electron beam drawing apparatus 7.
The data transfer between the data transfer apparatus 5 and the electron beam drawing apparatus 7 has been performed, in order to assure a band for transferring a large volume of control data, by dividing the control data and directly transferring each of the divided data from a plurality of interfaces provided in the data transfer apparatus 5 to a memory 71 of the electron beam drawing apparatus 7 via a plurality of dedicated buses each corresponding to each interface. For example, if it is assumed that the data transfer rate on one of the dedicated buses is 200 MB/s, when the data transfer rate exceeds 500 MB/s for the whole of control data, three interfaces 51a, 51b, and 51c and three dedicated buses 6a, 6b, and 6c are necessary.
The memory 71 is divided into three modules 71a, 71b, and 71c, each corresponding to each of the dedicated buses 6a, 6b, and 6c. Based on the divided data stored in each of the modules 71a, 71b, and 71c, a stripe is drawn by controlling the electron beam drawing apparatus 7 and moving a stage in the direction of the arrow in a frame F1. When drawing for one stripe data is completed with one of stripe data, the drawing stage is forwarded stepwise to a neighboring stripe region and drawing is performed based on stripe data assigned to a new stripe region. After that, by repeating the drawing operation while moving the stage continuously, a desired device pattern is drawn on a wafer.
However, the stage movement speed in the direction of drawing of the stripe is determined by the highest shot density in the stripe, and therefore, in the conventional transfer system described above, there has been a problem in that if the transfer of some of divided data is delayed, even if part of the memory is released, it is not possible to use the released memory sequentially because synchronization is taken in order to maintain the order of processing of the divided data, and as a result, the transfer of divided data is stopped and the processing time is wasted on the whole.
For example, in a frame F2 in FIG. 5, the shot density in a region II is much higher than that in regions I and III, and therefore, the stage movement speed of the frame F2 is determined by the region II.
The divided data corresponding to the region I are stored in the module 71a, the divided data corresponding to the region II are stored in the module 71b, and the divided data corresponding to the region III are stored in the module 71c. 
As a result, in the frame F2, even if the drawing processing in the regions I and III is completed, it is not possible to advance the drawing processing based on the next divided data to be transferred to the modules 71a and 71c until the drawing processing in the region II is completed and therefore there are no choices other than stopping the stepwise forwarding to the next stripe region.
In addition, since the memory of the electron beam drawing apparatus is directly connected in module units with the plurality of the dedicated buses in a one-to-one manner, there is also a problem in that the divided data to be transferred are restricted by the capacity of the memory (module). If data exceeding the memory capacity described above are transferred, there also arises a problem in that the processing of the electron beam drawing apparatus will be stopped.
The above-mentioned problems will occur similarly in data transfer systems in which a large volume of control data are divided and the order of processing of the divided data needs to be controlled, not limited only to the electron beam drawing apparatus.